GitLab

1. Renamed FakeSocket to FakeStreamSocket and FakeUdpSocket to
   FakeDatagramSocket,
2. Added factories for both stream and datagram fake
   sockets,
3. Move fake sockets to separate files out of fake_session.h

BUG=402993

Review URL: https://codereview.chromium.org/580243003

Cr-Commit-Position: refs/heads/master@{#296270}